Evaporation and condensation heat transfer and pressure drop in horizontal, 12.7-mm micro-fin tubes with Refrigerant 22
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Using R-22 as the fluid, a series of tests was performed to determine the evaporation and condensation performance of three 12.7-mm outside diameter tubes having many small, spiral inner-fins. The tubes, referred to as micro-fin tubes, had an 11.7-mm maximum inside diameter, 60 or 70 fins with heights ranging from 0.15 to 0.30 mm, and spiral angles from 15 to 25 deg. A smooth tube was also tested to establish a basis of comparison. The test apparatus had a straight, horizontal test section with a length of 3.67 m and was heated or cooled by water circulated in a surrounding annulus. Nominal evaporation conditions were 0 to 5°C (0.5 to 0.6 MPa) with inlet and outlet qualities of 15% and 85%, respectively; condensation conditions were 39 to 42°C (1.5 to 1.6 MPa) with inlet and outlet qualities of 85% and 10%, respectively. Mass flux varied from 75 to 400 kg/m2.s. The average heat transfer coefficents in the micro-fin tubes, based on a nominal equivalent smooth tube area, were 1.6 to 2.2 times larger for evaporation and 1.5 to 2.0 times drop increased, but by a smaller factor than the heat transfer coefficient.
author list (cited authors)
Schlager, L. M., Pate, M. B., & Bergles, A. E.